Allergy is a sensitive state of a living body owing to an antigen-antibody reaction. Allergies are classified into four types, type I to type IV, depending upon the reaction mechanism. Bronchial asthma, allergic rhinitis, urticaria, etc. which are representative allergic diseases from which many people suffer are due to a type I allergic reaction. A type I allergic reaction is an immediate type or an anaphylactic type reaction. In the type I allergic reaction, a degranulation takes place when antigen is bonded with IgE which is bonded with the cell surface of basophiles and mastocytes. Various allergic symptoms result when inflammatory mediators such as histamine and leucotriene are released.
For example, the allergic rhinitis from which increasing people suffer in recent years is classified into: 1) a whole-year allergy in which house dust is the main antigen, and 2) a seasonal allergy (pollinosis) primarily caused by pollen of Japanese cedar. The former starts when one is a baby or a small child and its symptoms continue. Accordingly, a continuous therapy is particularly necessary resulting in a demand for therapeutic and preventive agents which can be administered for long periods of time and which exhibit little side effect. In the case of rhinitis such as allergic rhinitis, it is an important therapy to remove unpleasant sensations caused by a promotion of secretion of nasal mucus. Therefore, an excellent agent for inhibiting the secretion of nasal mucus can be used as an effective therapeutic agent for rhinitis.
With respect to the pharmacological action of purine derivatives, Examined Japanese Patent Publications 58,726/85 and 26,527/86 disclose that 2,8-dihydroxypurine exhibits analgesic, sedative and antiallergic actions. Unfortunately this compound exhibits very poor solubility in both aqueous and nonaqueous solvents. For practical use as a drug, the compound has very little applicability.
The present inventors have found purine derivatives which are therapeutic agents for rhinitis which can be administered for long periods of time. The purine derivatives of the present invention exhibit an excellent action for inhibiting the secretion of nasal mucus. The compounds are more soluble in various solvents compared to the solubility of 2,8-dihydroxypurine. The present invention provides compounds which are readily soluble in aqueous solvents and which are readily absorbed into the bloodstream.